Field of the Invention
The present invention relates to a method of hydrolyzing using at least one glycosidase, a method for treating biofuel, and biofuel obtained by this method.
Description of Related Art
The use of renewable biofuel has increased rapidly over the last decades, in particular in view of the problematic of global warming. Typical renewable resources for biofuel are vegetable oils such as rape seed oil, soy oil and other oils.
Biofuel, and here in particular biodiesel, is produced from crude vegetable oil such as rape seed oil, soy bean oil or Jatropha oil by a degumming step, in which phospholipids are removed from the oil either chemically or enzymatically followed by a transesterification step, wherein the triacylglycerols contained in the vegetable oil are reacted with methanol and undergo thereby a transesterification step for producing glycerol and fatty acid methyl esters. Subsequently, the glycerol is removed and the fatty acid methyl esters form the biodiesel which can replace the mineral oils typically used.
Vegetable oils usually contain the phytochemicals acylated steryl glycosides (ASG) and steryl glycosides (SG), whereby the latter ones are not soluble in fatty acid alkyl esters (biodiesel). Steryl glycosides precipitate and may result in a filter clogging and/or causing an engine fueled by the biofuel to stop. Acylated steryl glycosides are transformed into the poorly soluble steryl glycosides during the transesterification step of the biodiesel production process. This in turn leads to an increase of the amount of insoluble and precipitated steryl glycosides and the problems associated therewith.
The steryl glycoside may precipitate during storage over the course of several weeks. Thus, although freshly produced biodiesel may meet the quality standards, after some weeks of storage the biodiesel may no longer pass the filter test and can thus not any longer be used.
Several approaches have been applied in the past for solving the problem of steryl glycosides precipitation during the biodiesel production. One approach is the application of an additional filtration step and/or centrifugation steps. The disadvantages of removing steryl glycosides by filtration or centrifugation are in particular the relative high costs associated therewith and the time required.
Further alternative approaches for removing steryl glycosides comprise the application of enzymes for hydrolyzing the steryl glycosides. EP 2098585 A1 (WO 2009/106360 A2) applies enzymatic hydrolysis for removing steryl glycosides by converting said steryl glycosides into more soluble free sterols and sugars. The enzymes suggested to be used are amongst others acylases, transesterases, transferases or hydrolases such as glycosidases, in particular beta-glucosidases, beta-glucanases, chitinases and cellulases.
A similar approach for removing steryl glycosides is reported in WO 2010/004423 A2 wherein glycosidases, glucosidases or amyloglucosidases are used for hydrolyzing the glycosidic bond in steryl glucosides such that the amount of steryl glucosides is reduced in oil, fat or biofuel.
WO 2010/102952 A1 describes a further alternative approach for removing steryl glycosides in fatty acid alkyl esters wherein the steryl glycosides are enzymatically acylated after transesterification resulting in acylated steryl glycosides, which do not precipitate in fatty acid alkyl esters (biodiesel). The enzymes used are mainly lipases or are preferably lipases or acyltransferases.
The methods applied for removing steryl glycosides, in particular the methods for enzymatic conversion of steryl glycosides, are focusing on processes after the transesterification process in the course of biodiesel production. Furthermore, said methods deal with the hydrolysis and conversion of steryl glycosides only.
As previously mentioned acylated steryl glycosides (ASG) are converted during the transesterification step in the biofuel production into steryl glycosides (i.e. without the fatty acid moiety), which are insoluble in biodiesel leading to precipitation resulting in filter plugging. As mentioned, the present methods focus on the enzymatic hydrolysis of acylated steryl glycosides. So far, no method or enzyme has been reported which is able to directly degrade or hydrolyze acylated steryl glycosides.